Power steering mechanism



J. O. SARTO POWER STEERING MECHANISM July 15, 1952 2 SHEETS-SEE! 1 Filed Oct. 28, 1949 INVENTOR. firmd 0. Gaffe.

,yrrafiwz'xsz 2 SHEETS SHEET 2 J. O. SARTO POWER STEERING MECHANISM INVENTOR. L/Zrmd 0; $4710.

July 15, 1952 Filed Oct. 28, 1949 Patented July 15, 1952 2,603,065 rowan srusnmo MECHANISM J orma O. Sarto, .Walled Lake, Mich, assignor to Chrysler Corporation, Highland Park, Mich, a corporation of Delaware Application October 28, 1949, Serial No. 124,006 6Clain1s. (01. 60-52).

The present invention relates to pressure fluid apparatus and systems employed in the operation of such apparatus and more particularly to improvements in power steering mechanism by means of which vehicle wheels are power-urged to follow motion of the vehicle steering wheel and to be steeringly deflected accordingly.

Power steering mechanisms are ordinarily looked on as including means for circulating power fluid such as oil, glycerin, or the like through a series of elements including areservoir, a power pump which draws fluid from the reservoir, and a power cylinder or motor to which fluid is delivered by the pump to actuate the steering mechanism. The power fluid from the steering mechanism is preferably returned to the reservoir for recirculation.- The steering mechanisms such as hereinafter described are preferably of the open valve type, that is so constructed that when the mechanism is idle there is a free passage therethrough for the power fluid such that the pump works only under a sufficient load to overcome the fluid frictionof the power fluid in the pipes and passages through which each circulates. Thus practically all the energy output of the effective fluid delivered by the pump is converted into useful work of steering when steering is being done instead of being wasted in overcoming back pressure set up by a relief valve when the steering mechanism is idle. that to be described, a sensitive followup mo: tion is effected between a sliding element connected for movement with the steering wheel and a second sliding element connected for movement with the steered part of the vehicle. 1 Y

' supporting the power plant and having a front These two sliding elements have a normal or a neutral relative position and when so situate,

no fluid power is exerted as on the steered part V to a neutral position relative to the other ele-v ment;

According to one feature of the present invention there is provision of 'an'improved means for controlling the power fluid effectively deliv- In mechanisms such as ered to the actual steering mechanism from the pump; though the flow and pressure of the pressure fluid may fluctuate at its pumping source, the fluctuations are reduced to substantially of no effect on the steering mechanism. According to a further feature, pump horsepower is effectively conserved such that undue quantities of fluid are not needlessly circulated through the open valve steering mechanism; moreover, swishing and swirling noises attendant with excessive quantities of fluid circulated through the steering mechanism and its associated conduit are reduced to a minimum.

According to anotherfeature, additional means is provided to limit the pressures in thelines attainable by fluid at any ratesiof flow allowed in the system regardless of the magnitude of flow and timeaocordingly which would be required to do, damage or otherwise accomplish undesirable results as respects the system.

According to still another feature of the invention, an. ordinary fixed displacement pump may be utilized to furnish motive fluid even though driven at speeds proportionate to fluctuating engine speeds. Y

According to still a furtherfeature the system tends to operate relatively quietly at advanced engine and corresponding pump speeds by virtue of theimproved regulating apparatus provided therefor.

These features as well as other objects and advantageswill be apparent from the following description with referencebeing had to the accompanying drawings wherein a preferred form of embodiment of the invention is clearly shown and in which:

Figure l is a fragmentary elevational' view of a vehicle to, which the invention has been applied;

and 1 Figure 2, is. a schematic diagramof the in vention showing actual mechanism involved in its operation.

In the drawings a vehicle illustrative of a general type to which the invention may be ap-'- plied is shown as having a steering wheel III. a propulsion power plant l2, a radiator core 14 for cooling the powerplant, and a frame [6 for portion it. Mounted by a controlled suspension, notshown, to front portion l8 of the frame may be steerable wheels 20 and 22. A link 24,

1 the motivating force for which will be laterset forth in detail, is adapted to steer awheel' of the vehicle by means of a steering knuckle, not shown. Movement of' one wheel may be transmitted to the opposite wheel by conventional means of rods,

3 further steering knuckles and the like associated therebetween. The header portion of radiator core M may have'a filler cap 26 and an intake fitting 28 associated with a tube or hose 30. A thermostat fitting 32 is connected to hose 30 and securely mounted to the casing of a circulating water pump ill for the'power plant. A circulating fan 36 may be carried by a shaft 38 which mutually drives the impeller of pump 34. Associated with the sheave it} of drivingshaft 38 is abelt 62 powered by the engine crankshaft, not shown, and having a portion 54 wrapped in an are around sheave 49. Another portion of the belt is indicated at 26 as being led through a sheave it carried by a shaft 5!! journalled in a bracket 52 mounted to the engine. Shaft 52 is drivingly connected to another shaft 56 by a coupling 54 which may be of the Oldham type or may constitute a friction type clutch adapted to slip under conditions of overload. Shaft 56 in turn drives a pum 58 chosen for purposes of illustration as of the positive displacement gear type. By virtue of the fact that belt 42 is driven in correspondence with engine speeds and shaft 56 varies in its speed likewise, the pump 58 will be driven at a speed proportionate to engine speed. Drive gear 60 carried by shaft 56 has teeth 62 which may mesh with corresponding: teeth 64 formed on a so-called idler Dump gear 66 journalled freely in the pump casing 58 by a shaft 68. The pump intake is connected by conduit 10 to a reservoir or container 12 provided with a filler and vent cap 14. Connected with the pump outlet is a conduit 16 from which a conduit 18 leads back to container 12. Interposed in conduit 19 is a valve 80 serving suitably as a shut-off valve. Additionally located in conduit 18 is a relief valve 82 wherein is defined an opening formed by seat structure 84 and 86. A shiftable'valving part 88 may be constrained in its movement at a guide location 90 such as to block in one position the valve seating opening at 84 and 86. In the eventuality of higher pressures in the valve seat opening, the shiftable valving part 88 will be tended to move in the direction of spring 92 thereby compressing it resiliently between the seat member 94 and the valving part 88. By means of a threaded stem 96 and an element 98, which may be hand operated, the preset spring force may be regulated in order to control the pressure at which valve 82 will relieve the pump outlet pressure. Conduit 16 may be provided with a fitting I at the regulator casing I02. A conduit I04 attached by a fitting I06 to casing I02 forms a return line to container 12. Within the regulator casing I02 an orifice is provided between an upstream passage H0 and a downstream passage II2. Adjacent these passages may be formed a chamber II4 connected upstream by communication H6 and downstream by communication I I 8. A valve opening I20 formed in the chamber 4' receives a valve I22 which may be of needle construction mounted on a stem I24. Exposed to upstream pressure is a surface I26 formed on a control member I28 connected for movement with valve stem I24. An opposed surface on member I28 is indicated at I30 and is exposed to pressure from the downstream side of orifice I08. It is apparent that the valve controlling member I28 may be subjected to a pressure differential against which a resilient member I32 will tend to exert an opposing force. Member I32 is adapted to act between surface I30 on valve control member I28 and a surface I34 in chamber II4. At the lower end of passage II2 on the downstream side of the orifice is a passage I36 leading to a fitting I38 having a conduit I40 associated therewith. A fitting I42 serves to connect the remote end of conduit I40 with the mechanism casing I44.

Steering wheel I0 has a hub I48 carried by a steering post or column I50. Worm member I52 on the steering column is formed with teeth I54 and has a reduced end I56 received in a suitable bearing I58 disposed in a bore I60 formed in steering gear casing I62. Casing I62 defines a cavity I64 appropriately to be supplied with a lubricant which may be introduced upon removal of closure I66 provided for the casing. A polygonal shaft I68 appropriately journalled in casing I62 has in association therewith a part I12 provided with a complementary polygonal surface I14. Part I12 constitutes one portion of an arm I16 and has a fork comprising members I18 and I which may adjustably be drawn together by a bolt I82 to bring the aforesaid polygonal surfaces into intimate engagement. Arm I16 and shaft I68 rotate in unison with a gear sector I84 .formed with teeth I86 meshing with the teeth of worm I52. Lower portion I81 of arm I16 has associated with it a link I which is connected at its end I88 thereto by a pivot I92. Link I90 at its opposite end I94 is connected by pivot I96 to a valve stem I98. The valve stem is slidably received in a sealed relation through an opening I99 formed in the end wall I91 of the mechanism casing I44. Valving parts 200 and 202, mutually connected by rod 204, are moved with shift of valve stem I98. The extreme faces of valving parts 200 and 202 may be effectively connected for pressure equalization by a drilled passage 206 running for a length of the valve stem I98 and rod 204. The extreme face 208 of valving part 200 will be seen to be in adjacency with a passage 203 and the inner face of valving part 200 will be seen to adjoin a similar passage 20I. The valving part 200 may be positioned variably to restrict a selected one of these passages only at the expense of variably opening the other; a similarly situated face 2I0 on valving part 202 may serve to restrict another passage 201. The counterpart passage for valving part 202 will be seen at 205. The valving parts just described are received in a shiftable sleeve 2I2 provided in the chamber 2I4 defined by walls 2I6 of casing I44. Sleeve 2 I2 is provided with an opening 2 I1 registering with a passage 2I8 leading to conduit I40. Openings 2 I6 and 2 I8 may be seen provided in other respective regions of sleeve 2I2. Communicating with the latter two openings are walls 220 V and 222 providing communication into a chamber 224 occupied by a slidable piston 226. The surface 228 of the piston is exposed to pressure in the passage defined by the wall structure 220 and the face 230 of the piston is exposed to pressure existing in the passage formed by wall structure 222. A piston rod 232 serves to guide piston 226 and is received in a guide-forming structure 234 formed in casing I44. By virtue of the pin and slot connection at 236 and 238, a rotatable link 240 is connected for movement with piston rod 232. Rotation of link 240 is about its pivot 242 held firmly in a portion 244 of casing I44. The upper end 246 of link 240 may be provided with a slot in which a pin 250 carried by yoke 248 is longitudinally slidable. The yoke just described is carried for movement with sleeve 2 I2 to the end that sleeve 2I2 moves in accordance with piston 226.

A reduced end 252 of the piston rod is received in an opening 254 formed in an end wall 255 of the casing for the steering mechanism. A pack-' ing element 256 is fitted around opening 254 and held there by a retainer 258. A rack segment 260 is carried by the piston rod and mounts teeth 262 enmeshed with cooperating teeth 264 formed on a gear sector 266. The gear sector 266 has a hub 268 rotatably carried in the steering mechanism casing by a rock shaft 210. An arm 212 connected for movement with gear sector 266 is provided at its depending end 214 with a connector 216 by means of which a pivot joint is effected with link 24. In the end wall I91 of casing I44 may be provided a fitting 282 by means of which a conduit 280 constituting a return to container 12 is connected. In the opposite end wall 255 another conduit 2?8 is provided, for effectin another return connection from casing I44 to container12, v In operation, the steering column I50 of the steering mechanism answers to movement of the operator-controlled steering wheel II) to. rotate worm I52. If the steering wheel is turned in a direction indicative of a right hand turn of the vehicle, worm I52 tends to thrust in the direction of bearing I58 yet is generally constrained from axial movement by easing I52. If the Worm is rotated in the opposite direction the axial thrust is then taken in the opposite direction as respects steering gear casing I62. By appropriate movement of the steering wheel, gear sector I84 may be caused to rotate about the axis of its rock shaft I88 and to move with it the arm I16. As arm ITS moves, accordingly moves valve stem I98 and the valve parts at either end of the valve rod 29 In neutral position valving parts 200 and 202 will tend to provide correspondingly open passages at am and 295 and correspondingly open passages at 263 and 201. Pressure fluid therefore, may enter the chamber 2M in the vicinity of valve rod 264 and the resulting flow will be diverted through series passages 20I and 293 and through series passages 205 and-201. The drains 213 and 23B serve to return the pressure fluid to container '12. The foregoing is a characteristic of the so-called open valve steering mechanisms. Let it be assumed that arm lie is caused to rotate clockwise due to appropriate motion by the operator of steering wheel If). valving parts 2% and 292 will move to the left in the direction of casing wall I91. Passage 203 will be restricted by the face 208 of valving part 26% and at the same time passage 295 will be given a larger effective area. Accordingly, the pressure exerted against face 228 of piston 22% will increase. As valving part 200 and valving rod 2% move, the valving part 202 will in turn additionally restrict passage 205 and increase the effective area of the passage 201. A decrease in pressure will, therefore, be experienced along the face 230 of piston 226. Owing to the unbalanced forces on its faces, piston 225 will tend to move in the direction to the right toward end wall 255 of casing hi4. ingly piston rod 232 will cause link 240 to be rotated counterclockwise and will likewise cause arm 272 to be rotated counterclockwise. Then not only do the steerable wheels of the vehicle tend to deflect in response to force exerted by link 24 but the sleeve 2I2 cooperating with the valving parts is shifted to the left toward end wall I91 of easing Hi l. It follows then that as the steerable Wheels move in answer to the steering wheel, the valve sleeve 2l2 likewise moves with the result of restoring the normal or relatively neutral status of disposition to the valving. In the-eventuality that the steerable wheels of the vehicle and the sleeve 2!? should overtravel the neutral position of the valve, an opposite force differential will prevail in the pi ton chamber 224 and the pressure fluid will be so exerted as to bring back the sleeve and steerable wheels to neutral position.

As previously noted, pump 53 is rotated at a speed roughly proportional to engine speed. At higher engine speeds the pump will naturally tend to deliver fluid at higher rates of flow. In.- asmuch as at high speeds a slight deflection of the road wheels will cause a rapid response as to turning effect on the vehicle, it is undesirable that the road wheels deflect any faster at high Accord speeds than at ordinary low speeds of the 've-' hicle. The regulating device I02 serves'to compensate for any increase in rate of flow of fluid due to the increase of the engine speed of the vehicle and fluid pump speed. As based on a known formula for orifice flow where the volume of fluid flowing is proportional to a fractional power of the pressure differential existing across the orifice, the regulator I02 is arranged so as to be sensitive to the pressure difierential. across its self-imposed orifice I08. As the flow increases through the orifice N3- the pressure' differential of the upstream side I it! overthe lower .istream side I I2 becomes more pronounced and a greater unbalance of pressure forces is-exerted. on'the faces of valve controlling member I28 ient element-i32 may be so calibrated asto be equal and opposite to the differential pressure force exerted on valve member I28 at. a: predetermined flow. Since, as stated,.the rate. of flow through orifice .IGB varies with the pressure differential taken to a fractional power, the valve stem I24 and valve I22 move substantially Without regard to any one existing pressure in the system or over the entire system but are responsive merely to pressure differential and rate of flow of the fluid for all practical purposes. When the rate of flow of fluid passing from passage I II) to I I2 exceeds the predetermined value then the pressure difierential over the orifice will have increased in a manner which may be roughly equal to the square of the rate of flow. Then the pressure differential resulting therefrom tends to overcome the resistance of resilient spring I32 and allow pressure fluid to by-pass the pump and return to the container I2 by means of conduit I-ilfil. If the flow through orifice I08 islagain increased. the further increase in the pressure differential will cause the valve I22 to oifer even less of a restrictive effect in return line I04 and by-pass further of the fuel. The change of the pressure differential is sufficient over the ordinary range of flows to hold the rate of flow of fluid in downstream passage I I2 to within fairly close limits. Inasmuch as the regulator I02 will ordinarily be connected adjacent pump 58 or else made integral therewith such that conduit I04 discharges directlyinto the inlet of thepump, there will be no substantial amount of fluid allowed to. circulate in the steering mechanism system above the predetermined amount desired. Without excessive flow rates through the so-called openvalve type steering mechanism, the steering .opera.-.

tion either in the valve neutral or the valve operating position will be relatively quiet. Moreover,

In view of the fact that pump 58 is a positivedisplacement pump, it will be appreciated that at either high or low speeds thereof, a continuous amount of fluid will pass through the pump. If

for some reason the steerable wheelsdo not' respond to fluid pressure such as in the instance of the vehicle being parked against a curb so that the wheels cannot turn, the positively di placed fluid will need a meansiof escape inthe pressure system or the pressure will tend to 1111-. crease. The relief valve 82 serves to relieve the system in this contingency. Rather than having,

the fluid circulate at excessive pressures, the valving part 88 will be caused to unseat and to Resilv by-pass the pump fluid through conduits 18 to container 12.

It is apparent then that under conditions of excessive pressure in the system the effective rate of flow of fluid in conduit 16 to the regulator I02 is eventually limited by the relief valve 82 with pressures other than abnormal and excessive flow through orifice I08, the eifective flow is limited by the regulator 102 to a predetermined maximum within reasonable limits and the excess fluid is passed through conduit I04 back to container 12. In both instances the fluid diverted from the effective flow of fluid is by-passed to reservoir. It will be recognized from the fore going that a steering mechanism has been provided which will cause a substantial duplication of motion in' the steerable wheels as respects any initiating movement in the steering wheel, The automatic regulating controls shown serve to regulate the motive fluid'flowing to the steering mechanism notwithstanding variations in the character of operation of the pressure fluid supply means. In the latter regard a fixed displacement pump, which happens to be the device 58 selected for illustration, can be readily utilized even though driven at speeds variable with the speed of the engine in the vehicle.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is tobe understood that other forms and modifications in structure might be adopted such as will readily occur to those skilled in the art but nevertheless coming within the scope of the present invention.

What is claimed is:

1. For use with a vehicle characterized by a propulsion motor and steering mechanism: in combination, a valve-controlled fluid motor having a controlled normal at-restcondition and having a controlled in-motion condition for providing power to turn the steering mechanism, the valve unit of said fluid motor being operatively arranged for receiving a continuous flow of power fluid regardless of the controlled condition being maintained aforesaid, a positive displacement pump unit driven at a speed proportional to the speed of the propulsion motor for providing power fluid to the fluid motor under said conditions and being'relatively unloaded when said motor is at rest and being loaded by said motor when said motor is set in motion, and conduit structure comprising communication between said units provided with an orifice, a bypass chamber in a separated position as respects said orifice and having a discharge opening, a spaced pair of passageways communicating fluid pressures from either side of said orifice to said bypass chamber and of which'one passageway is relatively adjacent said discharge opening and the other said passageway is relatively remote to said discharge opening, valving intervening in said bypass chamber between said paired passageways adjustably restricting the discharge opening-adjacent said one passageway, said valving being arranged to present certain surfaces exposed to the fluid pressure from said one passageway side of the orificeand opposed surfaces exposed to the fluid pressure from the other said passageway side of the orifice, and to tend to decrease the amount of restriction in said discharge opening with increasing pressure differential across the orifice, and a fluid relief line establishing communication with said communication between said units, on the said one passageway side of the orifice.

'- 2. In a motor-propelledvehicle having a propulsion motor, a fluid pressure system comprising a positive displacement pump part driven at a speed proportionate to the speed of the propulsion motor and having a fluid supply, power steering mechanism including a fluid motor having a valving part associated therewith for accommodating a continuous flow of motive fluid and utilizing a predetermined minimum flow therefrom for the efiective operation of the said mechanism, said valving part having neutral and motor-motivating positions for causing the fluid motor to set the power steering in motion and at rest selectively while accommodating the above described continuous flow of motive fluid, fluid flow means for so connecting said parts as to deliver substantially only said predetermined minimum flow to the valving part and motor from the pump, said fluid flow means comprising flow communication between said parts, a calibrated orifice interposed in said communication, first means presenting a movable valving surface having a closed position, a bypass leading from the communication adjacent the orifice and being closed by said valving surface of said first means when the latter is in said closed position, said valving surface being movable into a position effecting the opening of said bypass, and second means associated with the first means comprising an opposed pair of actuating portions responsive one to fluid pressure upstream of said orifice and the other to fluid pressure downstream of said orifice and arranged for efiecting movement of the valving surface and opening of the bypass incident to a pressure drop across the calibrated orifice indicative of attainment of said predetermined minimum flow through the communication to the valving part and accommodated by the communication when the said valving part is in any one of the neutral and motor motivating positions aforesaid.

3. In a motor-propelled vehicle having a propulsion motor, a fluid pressure system comprising a positive displacement pump part driven at a speed proportionate to the speed of the propulsion motor and having a fluid supply, power steering mechanism including a fluid motor having a valving part associated therewith for accommodating a continuous flow of motive fluid and utilizing a predetermined minimum flow therefrom for the effective operation of the said mechanism, said valving part having neutral and motor-motivating positions for causing the fluid motor to set the power steering in motion and at rest selectively while accommodating the above described continuous flow of motive fluid, fluid flow means for so connecting said parts as to deliver substantially only said predetermined minimum flow to the valving part and motor from the pump, said fluid flow means comprising flow communication between said parts, a calibrated orifice interposed in said communication, first means presenting a movable valving surface having a closed position, a bypass leading from the communication adjacent the orifice and being closed by said valving surface of said first means when the latter is in said closed position, said valving surface being movable into a position effecting the opening of said bypass, and second means associated with the first means comprising an opposed pair of actuating portions responsive one to fluid pressure upstream of said orifice and the other to fluid pressure downstream of said orifice and arranged for eifecting movement of the valving surface and opening of the bypass incident to a pressure drop across the calibrated orifice indicative of attainment of said predetermined minimum flow through the communication to the valving part and accommodated by the communication when the said valving part is in any one of the neutral and motor-motivating positions aforesaid, said first and second means being movable together in paths conforming to a common axis of motion and having associated therewith resilient means continually tending to produce the bias for urging the valving surface into closed position.

4. Fluid pressure system for a steerable automotive vehicle comprising a normally unactuated fluid pressure operated steering mechanism adapted to be actuated to move loads offering varying resistance, said steering mechanism having means on the intake side thereof forming a path for pressure fluid and having control valving therefor in said path continuously permitting said fluid to flow therethrough throughout the range of failing to apply any substantial pressure to leave the mechanism at rest and causing pressure to be applied to set the mechanism in motion both when relatively loaded and when relatively unloaded, said steering mechanism being arranged for performing desirably under conditions of predetermined pressure and rate of flow in the pressure fluid path, means adapted to deliver a supply of fluid under varying pressure communicating with said fluid path, bypasses providing for return of fluid from said fluid path back to the source of fluid supply, restrictive valving adjustable with respect to the bypasses having means sensitive to characteristics of the fluid associated therewith for opening a said bypass under highly resistive loadings on the steering mechanism creating back pressures in the fluid path arising to said predetermined pressure and for independently opening another said bypass in accordance only with rates of flow in said fluid path above said predetermined rate without regard to the degree of actuation of said steering mechanism through the pressure range aforesaid.

5. In an engine-propelled vehicle having a manually controlled steering gear and a steerable road wheel, a pump-driven hydraulic steering mechanism of the open valve type for turning said steerable road wheel in response to actuation of said manually controlled steering gear and otherwise permitting said driving pump to operate against substantially no resistance, said mechanism comprising means for mechanically connecting the driving pump to the vehicle engine to provide a direct mechanical drive therebetween whereby the pump is always driven at a speed proportional to the speed of the engine, a valving-controlled steering motor driven by the pump, said valving being controlled in response to the above-described steering gear actuation and having a neutral open-valve position permitting free circulation of the pump output against no substantial opposing pressure. said pump being a positive displacement pump having a fluid flow supply path and a fluid flow discharge path for carrying the effective output thereof and communicating with the valvingcontrolled steering motor, bypass between the respective flow paths of the pump for accom modating excessive flow from the pump above a predetermined rate of effective output to the steering motor, and flow control means forming an adjustable restriction with respect to the bypass, said flow control means including fixed and movable parts one of which is formed to 10 provide a pre-calibrated orifice in the pump effective output flow path, said fixed and mov able parts establishing cooperation with one another to open the bypass restriction adjustably in accordance with the magnitude of pressure differential across said pre-calibrated oriflce for limiting the effective output flow available to the open-valve type controlled steering motor to said predetermined rate throughout the operating range of the steering motor including the open-valve substantially unopposed condition thereof and throughout the speed range of the pump and vehicle engine.

6, In an engine-propelled vehicle having a manually controlled steering gear and a steerable road wheel, a pump-driven hydraulic steering mechanism of the open valve type for turning said steerable road wheel in response to actuation of said manually controlled steering gear and otherwise permitting said driving pump to operate against substantially no resistance, said mechanism comprising means for mechanically connecting the driving pump to the vehicle engine to provide a direct mechanical drive therebetween whereby the pump is always driven at a speed proportional to the speed of the engine, a valving-controlled steering motor driven by the pump, said valving being controlled in response to the above described steering gear actuation and having a neutral open-valve position permitting free circulation of the pump output against no substantial opposing pressure, said pump being a positive displacement pump having a fluid flow supply path and a fluid flow discharge path for carrying the effective output thereof and communicating with the valvingcontrolled steering motor, bypass between the respective flow paths of the pump for accommodating excessive flow from the pump above a predetermined rate of effective output to the steering motor, flow control means forming an adjustable restriction with respect to the bypass, said flow control means including fixed and movable parts one of which is formed to provide a pro-calibrated orifice in the pump effective output flow path, said fixed and movable parts establishing cooperation with one another to open the bypass restriction adjustably in accordance with the magnitude of pressure differential across said pre-calibrated orifice for limiting the effective output flow available to the open-valve type controlled steering motor to said predetermined rate throughout the operating range of the steering motor including the openvalve substantially unopposed condition thereof and throughout the speed range of the pump and vehicle engine, and a relief communication between said respective flow paths of the pump operated independently of said bypass for preventing excessive output flow pressures.

JORMA O. SARTO.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITflD STATES PATENTS Number Name Date Re. 19,515 Bragg Apr. 9, 1935 1,467,522 Amsler Sept. 11, 1923 1,914,267 Leupold June 13, 1933 2,102,865 Vickers Dec. 21, 1937 2,382,866 Edge Aug. 14, 1945 2,408,770 Frische Oct. 8, 1946 

